This invention relates to an apparatus for the introduction of finely divided coal solids into a vessel in a carefully controlled reliable manner.
Particulate solids material, particularly finely divided particulate solids must be frequently handled in chemical processes. For example, in coal conversion, the art is replete with examples for the conversion of finely divided coal material into a more valuable gaseous product. Traditionally, particulate solids, such as coal solids, are transferred or discharged from a storage or reaction vessel to a vertical tube called a standpipe. The solids flow rate through the standpipe is generally controlled by a slide valve, cone valve, trickle valve, screw feeder or other similar mechanical device positioned at the bottom of the standpipe. A problem commonly associated with these mechanical devices is their propensity to plug when the solid materials, i.e. coal, contained therein are exposed to moderate or high temperatures and pressures. In addition, these mechanical valve devices, when installed in an overall process, are inevitably placed in relatively inaccessible locations. Accordingly, when these mechanical devices plug, as they frequently do, they are difficult to unplug or repair because of their inaccessability. In addition, particulate solids are generally very abrasive. As a result, mechanical devices requiring movement between valve components must utilize expensive material for construction so that the mechanical valve does not become rapidly corroded.
The problems associated with mechanical errosion and valve plugging are particularly vexatious when such valves are utilized in conjunction with the high temperatures and pressures utilized in modern processes for the gasification of coal. For example, most coal has a substantial tendency to agglomerate or stick when exposed to high temperatures. As a result, coal, which has been substantially reduced in size, when exposed to high temperatures, agglomerates and becomes sticky when exposed to high temperatures. The advantages of the original comminution step used pulverizing the coal have been diminished and, just as importantly, the coal has a tendency to agglomerate or stick to the apparatus per se. In an effort to remove some of these agglomeration problems, the art has attempted to introduce the coal into the reaction bed at a point far removed from the high temperature associated with the coal gasification reaction. For example, the prior art traditionally introduces the finely divided particulate coal into the free space that is present above the fluidized bed contained in the lower portion of the reactor. This method of introduction results in diminished conversion of coal to gas products because the upward velocity of the gas emitted from the fluid gasification bed generally sweeps with it fine particles in the feed material. As a result, these fine coal particles are carried out of the reaction zone and are not converted therein to gaseous products. Although these fines can be recovered in downstream processing equipment and then returned to the reaction zone, this is not an efficient method of conversion since it increases the cost of downstream processing equipment.
Because of these problems associated with mechanical valve arrangements, the prior art has endeavored to develop improved methods of transferring solid materials in a controlled manner. For example, in Lapple, U.S. Pat. No. 2,684,869, there is described an apparatus for handling pulverulent material which comprises a vertical pipe connected to a horizontal pipe section via a standard pipe tee. According to the teachings of Lapple, gas is introduced into the bottom portion of the tee at a point which represents a discontinuity in the flow path of the solids through the apparatus. Because of the general geometry and discontinuities associated with the Lapple apparatus, high flow rates are not attainable through the Lapple apparatus. In fact, the dead spaces contained in the Lapple apparatus and adjacent in the introduction point for the gas utilized to transport the pulverulent material, when used in a coal gasification environment, can cause coal to accumulate and agglomerate therein, thus leading to unreliable control over the solids flowing through the apparatus. In addition, the Lapple apparatus requires the introduction of appreciable gas volumes to produce the desired flow rate through the apparatus.
Several "valves" are illustrated in Perry's Chemical Engineers Handbook, Fourth Edition, pages 20-47 through 20-49. For example, Perry illustrated an ICI valve which is described as serving better as a seal device than a solids control valve. As illustrated, the ICI "valve" comprises a generally vertical column. As a result, this ICI structure contains a dead spot or discontinuity in the bottom portion thereof which will interfere with efficient solids flow therethrough and, more particularly, in the case of coal processing, will produce a situs for inadvertent undesired coal agglomeration. It is clear that this ICI valve cannot reliably and efficiently and accurately control solids particularly in view of Perry's characterization of the valve as a seal device rather than a control valve.